Improved thermal control for apparatus for the manufacture of three-dimensional objects

ABSTRACT

An apparatus (1) for manufacturing a three-dimensional object from particulate material, the apparatus comprising: a work space (100) bounded by a first side wall (100A) on a first side of the work space, and a second side wall (100B) on a second side of the work space, the first side wall opposing the second side wall; a build bed (170) having a build bed surface (160), the build bed surface being comprised in the floor of the work space and having a first edge (160′) on the first side of the work space, towards the first side wall, and a second edge (160″) on the second side of the work space, towards the second side wall; a first gas inlet (101A) at or near the first side wall; a second gas inlet (101B) at or near the second side wall; a first gas outlet (102A) above the floor (100C) of the work space, the position of the first gas outlet being coincident with the first edge of the build bed surface, or between the first edge of the build bed surface and the first gas inlet; and a second gas outlet (102B) above the floor of the work space, the position of the second gas outlet being coincident with the second edge of the build bed surface, or between the second edge of the build bed surface and the second gas inlet; wherein the first gas outlet is positioned higher in the work space than the first gas inlet, and the second gas outlet is positioned higher in the work space than the second gas inlet; and wherein one or more flow devices (210, 211, 212) are operable to create first and second gas flows between the first gas inlet and the first gas outlet, and between the second gas inlet and the second gas outlet, respectively, such as to create respective first and second gas curtains on the first and second sides of the work space in use.

FIELD OF INVENTION

The present disclosure relates to an apparatus for manufacturing athree-dimensional object from particulate material and a method thereof,capable of improving thermal control.

BACKGROUND

In three-dimensional printing technology, three-dimensional objects canbe formed in a layer-wise manner using known methods or processes ofmanufacturing, such as selective laser sintering, selective lasermelting, electron beam melting and high speed sintering. In theseprocesses, layers of particulate material are successively spread on abuild bed surface of a build bed, and portions of successive layers areselectively solidified to form the layers of the three-dimensionalobject. Each layer of particulate material is selectively fused,sintered or melted by applying energy, heat or radiation, so thatlayer-by-layer the three-dimensional object is formed.

During a typical build process, the temperature of the build bed andtemperature of the components within the work space is prone tofluctuate, for example due to one or more of (a) a sintering lamp beingapplied intermittently across the build bed surface, leading to hot andcold periods; (b) a new (cooler) layer of particulate material beingapplied; (c) a preheat lamp being applied intermittently across thebuild bed surface; and (d) carriages on which a powder distributiondevice, printheads or lamps are mounted, comprising a hot surface andalso shielding the build bed surface intermittently from an overheadheater, passing across the build bed surface. While such an overheadheater may be used to dynamically compensate for such thermalfluctuations, it cannot actively cool the build bed surface, and anadditional level of thermal control is desirable.

Insufficient temperature control may lead to a lack of control of thebuild bed temperature which may result in warpage, shrinkage or curlingof the three-dimensional object due to thermal effects. Therefore, tocontrol the temperature of the layer and/or build bed surface and inturn to control the temperature of the build bed, it is desirable toremove excess heat from the apparatus in which the three-dimensionalobject is being built.

Furthermore, by-products such as airborne particles, smoke, dust orfumes may be formed in a work space during the three-dimensionalprinting process, and it is desirable to remove these from the workspace so as to avoid their build up within the work space environment.

SUMMARY

Aspects of the invention are set out in the appended independent claims,while particular embodiments of the invention are set out in theappended dependent claims.

The following disclosure describes, according to a first aspect of theinvention, an apparatus for manufacturing a three-dimensional objectfrom particulate material, the apparatus comprising: a work spacebounded by a first side wall on a first side of the work space, and asecond side wall on a second side of the work space, the first side wallopposing the second side wall; a build bed having a build bed surface,the build bed surface being comprised in the floor of the work space andhaving a first edge on the first side of the work space, towards thefirst side wall, and a second edge on the second side of the work space,towards the second side wall; a first gas inlet at or near the firstside wall; a second gas inlet at or near the second side wall; a firstgas outlet above the floor of the work space, the position of the firstgas outlet being coincident with the first edge of the build bedsurface, or between the first edge of the build bed surface and thefirst gas inlet; and a second gas outlet above the floor of the workspace, the position of the second gas outlet being coincident with thesecond edge of the build bed surface, or between the second edge of thebuild bed surface and the second gas inlet; wherein the first gas outletis positioned higher in the work space than the first gas inlet, and thesecond gas outlet is positioned higher in the work space than the secondgas inlet; and wherein one or more flow devices are operable to createfirst and second gas flows between the first gas inlet and the first gasoutlet, and between the second gas inlet and the second gas outlet,respectively, such as to create respective first and second gas curtainson the first and second sides of the work space in use.

By virtue of the above arrangement of the first and second gas inletsand the first and second gas outlets, and as a consequence of the firstand second gas curtains thus created on either side of the work space(the first and second gas curtains being outward from, or potentiallyaligned with, the first and second edges of the build bed surface),improved thermal control may be achieved during the manufacture ofthree-dimensional objects within the work space. Improved efficiency ofremoval of airborne species (e.g. particles, chemical substances,impurities, smoke, fumes, exhaust gases etc.) from above the build bedsurface may also be realised.

According to a second aspect of the invention, there is provided amethod for manufacturing a three-dimensional object from particulatematerial, the method being performed using the apparatus according tothe first aspect of the invention, and comprising: operating the one ormore flow devices to create first and second gas flows between the firstgas inlet and the first gas outlet, and between the second gas inlet andthe second gas outlet, respectively, such as to create the respectivefirst and second gas curtains on the first and second sides of the workspace.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now directed to the drawings, in which:

FIG. 1 is a schematic cross-sectional diagram of an apparatus forlayer-by-layer formation of three-dimensional objects according to anembodiment of the invention, including a work space, a build bed, firstand second gas inlets, and first and second gas outlets;

FIG. 2 is a plan view from above of the build bed, gas inlets and gasoutlets within an apparatus such as that of FIG. 1 ;

FIGS. 3(a)-(h) are schematic cross-sectional views of a first side of awork space such as that of FIG. 1 , showing alternative arrangements andgeometries of the first gas inlet;

FIG. 4 is a schematic cross-sectional view of a build bed and a workspace of an apparatus such as that of FIG. 1 , showing gas curtainsformed on first and second sides of the work space;

FIG. 5A is a schematic cross-sectional view of the build bed and workspace as depicted in FIG. 4 , together with an arrangement of a flowdevice that is coupled to both the first and second gas outlets;

FIG. 5B is a schematic cross-sectional view of an alternativearrangement to that of FIG. 5A, showing a first flow device that iscoupled to the first gas outlet and a second flow device that is coupledto the second gas outlet;

FIG. 6 is a schematic cross-sectional view of the build bed and workspace as depicted in FIG. 4 , and an illustration of gas flow above thebuild bed surface;

FIG. 7 is a schematic cross-sectional view of the build bed and workspace as depicted in FIG. 4 , and an arrangement of a gas duct with adownward flow of gas towards the build bed surface;

FIG. 8 is a schematic cross-sectional view of the build bed and workspace of an apparatus such as that of FIG. 1 , and an arrangement of adistribution sled on the first side of the work space and a print sledon the second side of the work space;

FIG. 9 is a schematic cross-sectional view of the build bed and workspace of an apparatus such as that of FIG. 1 , and an arrangement ofvarious guiding element(s) in the work space;

FIG. 10A-10B are schematic cross-sectional views of the first side ofthe work space, with alternative arrangements of guiding elements; and

FIG. 11 is a schematic cross-sectional view of a first side of a workspace such as that of FIG. 1 , showing a further alternative arrangementand geometry of the first gas outlet.

In the Figures, like elements are indicated by like reference numeralsthroughout. It should be noted that the drawings are not to scale andthat certain features may be shown with exaggerated sizes so that theseare more clearly visible.

DETAILED DESCRIPTION

The apparatus and method of the present disclosure enable improvedthermal control during the manufacture of three-dimensional objects.Improved efficiency of removal of airborne species (e.g. particles,chemical substances, impurities such as evaporating fluid agent, smoke,fumes, exhaust gases, etc.) from the apparatus may also be achieved.

By way of an initial overview, the present disclosure provides apparatuscomprising a first gas inlet and a second gas inlet, respectively onfirst and second sides of the work space, away from the build bedsurface; and first and second gas outlets above the floor of the workspace, respectively on the first and second sides of the work space, andpositioned such that they are closer to the build bed surface than tothe first and second gas inlets when viewed from above. This isillustrated in FIG. 2 which shows a plan view of the work space 100,first and second gas inlets 101A and 101B, and first and second gasoutlets 102A and 102B, looking down from above. As shown in FIG. 2 , thedistance between the build bed surface 160 and each of the first andsecond gas inlets 101A, 101B is depicted as “d1”, while the distancebetween the build bed surface 160 and each of the first and second gasoutlets 102A, 102B is depicted as “d2”. The gas inlets 101A, 101B andthe gas outlets 102A, 102B are arranged with respect to the build bedsurface such that the distance “d1” is greater than distance “d2” (i.e.d1>d2). Further, the first and second gas outlets 102A, 102B may becoincident with respective first and second sides 160A, 160B of thebuild bed surface 160 (i.e. such that d2=0), or may be located betweenthe respective first and second sides 160A, 160B of the build bedsurface 160 and the respective first and second gas inlets 101A, 101B(i.e. such that 0<d2<d1). In such arrangements, the gas flow is notdirected at the build bed surface 160, preventing direct impact of gasflow on the build bed surface 160 and hence avoiding any resultingthermal non-uniformities. However, the gas flow assists in cooling thebuild bed surface 160 and removing any airborne species.

Moreover, the present apparatus and method ensure that the gas flow or aventilation flow passes across the work space before the flow isextracted, particularly engaging with hot areas of the work space andremoving heat from them.

Reference will now be made in detail to the embodiments, examples ofwhich are illustrated in the accompanying drawings.

Apparatus Overview

FIG. 1 schematically illustrates a front view of an apparatus 1 for themanufacture of three-dimensional objects. The apparatus 1 is operable tofabricate three-dimensional objects from a particulate material, andincludes a supply module 110 for storing the particulate material, awork space 100 bounded by a first side wall 100A on a first side of thework space 100, a second side wall 100B on a second side of the workspace 100 (the second side opposing the first side), a floor 100C on abottom side of the work space 100 and a ceiling 100D on a top side ofthe work space 100. The apparatus 1 further comprises a work surface 190comprising a build bed surface 160 provided at the top of a build bed170 which is within a build chamber 200 wherein successive layers of thethree-dimensional object are formed; a distribution sled 130 operable todistribute a layer of particulate material within the build bed surface160; and one or more radiation source assemblies such as overheadradiation source assembly 150 and/or a traversing radiation sourceassembly (not shown), such as an electromagnetic radiation sourceassembly to preheat and/or to sinter the particulate material oralternatively a laser source (not shown), to sinter the particulatematerial to form each layer of the object. The work space 100 includesthe work surface 190, the distribution sled 130, the build bed surface160 and the overhead radiation source assembly 150.

The apparatus 1 may be a high speed sintering apparatus, and may furthercomprise a print sled operable to print (by means of one or more dropletdeposition heads) a fluid pattern comprising radiation absorbingmaterial (RAM) to define the cross-section of the three-dimensionalobject to be manufactured in that layer of particulate material.

As shown in FIG. 1 , the distribution sled 130 comprises bearingsmounted on rails 120. The rails 120 suspend the sled 130 above the worksurface 190 of the apparatus 1. The overhead radiation source assembly150, such as a ceramic heater, may be provided above the build bedsurface 160.

The apparatus 1 further comprises a first gas inlet 101A at or near thefirst side wall 100A, a second gas inlet 101B at or near the second sidewall 100B, and a first gas outlet 102A and a second gas outlet 102Babove the floor 100C of the work space 100.

It should be noted that the first side wall 100A and the second sidewall 100B are depicted in the figures as being the side walls of ahousing defining the work space, but this is merely for illustrativepurposes and for ease of understanding the invention. The invention isnot limited to this, and the first side wall 100A and/or the second sidewall 100B may instead be partial or full walls arranged inwardly fromthe walls of the housing itself. Moreover, the first side wall 100Aand/or the second side wall 100B may be hollow walls and the firstand/or second gas inlets 101A, 101B may be formed within those hollowwalls.

Further, the expression “at or near” in this disclosure should beinterpreted broadly, to encompass all possible arrangements of the gasinlets in proximity to the side walls. For example, the gas inlet couldbe “at” the side wall—e.g. the gas inlet may protrude as a nozzle fromthe side wall, or may be provided as a nozzle between the side wall andthe ceiling of the work space. Alternatively, the gas inlet(s) may be“in” the side wall—for example, the gas inlet may be an opening or holein the side wall. In a further alternative, the gas inlet may be “near”the side wall—for example, the gas inlet may be an outlet of a flexibleor a rigid pipe or tube which may be suspended from the ceiling of thework space near the side wall, or may be otherwise positioned betweenthe side wall and the ceiling of the work space.

To illustrate this, FIGS. 3(a) to 3(h) depict cross-sectional views ofthe first side 100A of the work space, and illustrate various possiblearrangements and geometries of the gas inlet 101A. It should of coursebe appreciated that FIGS. 3(a)-(h) depict only one side of the workspace; the other side of the work space may be (but need not be) amirror image of the shown side of the work space. The first and secondgas outlets 102A, 102B may have any of the configurations shown in FIGS.3(a)-(h), or variants thereof. Both the outlets may have the sameconfiguration, or may have different configurations.

In more detail, FIG. 3(a) shows a gas inlet 101A as an aperture or ahole in the side wall 100A. Alternatively, the or each gas inlet maycomprise a nozzle at the side wall. For example, FIGS. 3(b) to 3(f)depict a gas inlet 101A as a nozzle protruding from the first side wall100A into the first side of the work space.

In one variant the gas inlet 101A may be directed horizontally, parallelto the floor 100C of the work space 100, as shown in FIG. 3(b), so thatthe gas flow enters the work space parallel to the build bed surface.

In another variant, as shown in FIG. 3(c), the first and second gasinlets 101A, 101B may be angled downwards, towards the floor 100C of thework space 100, so as to direct the gas flow such that the gas flow isdeflected by the floor 100C of the work space 100 towards the first gasoutlet 102A and the second gas outlet 102B respectively. This may beadvantageous as the gas flow is projected towards the floor of the workspace, thereby covering, before extraction, a greater distance at thelevel of the build bed surface than with the arrangement shown in FIG.3(b), thereby more effectively extracting heat from the work space.

In another variant, as shown in FIG. 3(d), the first and second gasinlets 101A, 101B may be angled upwards towards the ceiling 100D of thework space 100, so as to direct the gas flow more directly towards thefirst gas outlet 102A and the second gas outlet 102B, thereby directingthe gas flow towards hot areas of the work space 100. Such hot areas mayfor example be the ceiling of the work space, the areas within the workspace where the radiation source assembly is located (e.g. on sleds), orthe areas within the work space which may be more likely impacted byheat or may be more prone to generated heat within the work space.

In variants where the first and/or second gas inlet is configured as anozzle or a pipe, the nozzle or the pipe may be adjustably mounted, toenable the user to select the angle of the first and/or second gas inletand thus the angle at which the gas flow will initially be directed.

In both the above arrangements of the first and second gas inlets 101A,101B, the first and second gas outlets 102A, 102B may be angled suchthat the gas flow between the inlets and the outlets is as smooth aspossible, with a non-turbulent overall line of gas flow.

It will be appreciated that the shape of the first and second gas inlets101A, 101B is not limited to being circular. Instead, they may have anyother shape, e.g. hexagonal, square, rectangular, tetragonal, polygonaletc. For example, the gas inlet may be conical and may have a taperedinlet as shown in FIG. 3(e) such that it spreads out the gas flow as itenters the work space. Alternatively the gas inlet may have anasymmetric shape, e.g. as shown in FIG. 3(f), or the gas inlets may forinstance be elongate slots. Moreover, the first and second inlets may beof any size—and may be the same size or different sizes as required.Further, the gas inlets 101A, 101B and/or the gas outlets 102A, 102B maybe of similar or dissimilar geometries.

In other variants the first and second gas inlets 101A, 101B maycomprise an elongated nozzle, a tube or a pipe through which gas mayenter the work space. For example, the gas inlet 101A may be an elongatenozzle arranged between the side wall 100A and the ceiling 100D of thework space 100 as shown in FIG. 3(g), or the gas inlet 101A may be aflexible or a rigid pipe that may be suspended from the ceiling 100D ofthe work space 100 as shown in FIG. 3(h). FIGS. 3(a)-3(h) are onlyexamples illustrating different types of inlet or outlet geometry (inall cases with the inlet 101A being “at or near” the side wall 100A),and an appropriate inlet or outlet geometry can be chosen according tothe work space dimensions and design. Further, one or more gas outletsmay be arranged at a right angle, an acute angle or an obtuse angle withrespect to the ceiling of the work space. For example, the outlet couldface sidewards towards the side wall comprising the respective gasinlet, or alternatively sidewards towards the opposite side wall of thework space.

Referring back to FIG. 1 , in an example process sequence, at the startof a cycle, a layer of particulate material is distributed on the buildbed surface 160 by the distribution sled 130. Any excess particulatematerial is fed into a return outlet 180 to recirculate into the systemor to collect in an external container. A fluid such as radiationabsorbing material (RAM) is then deposited onto the layer of particulatematerial by a print sled (not shown), to define the cross-section of thethree-dimensional object 300 to be manufactured in that layer, and thebuild bed surface 160 is then exposed to radiation from a radiationsource assembly to sinter the powder. Following sintering, the build bedsurface 160 is lowered by a layer thickness; this is considered to bethe end of the cycle. The next cycle begins with depositing anotherlayer of the particulate material on the build bed surface 160, and theprocess is repeated until the desired three-dimensional product has beenfabricated.

Implementations

FIG. 4 shows a schematic cross section of a build bed and a work spaceof an apparatus such as that of FIG. 1 . In FIG. 4 , a first edge of thebuild bed surface 160 is shown as 160′ while a second edge of the buildbed surface 160 is shown as 160″. The edges of the build bed surfacedefine a boundary of the build bed surface.

As shown in FIG. 4 , the line A-A′ indicates a section through the buildbed 170 (into the page). In the present disclosure, the sides of thework space are considered with respect to the section A-A′ of the buildbed 170. Thus, a first side of the work space is the side which is tothe left of the section A-A′, whereas a second side of the work space isthe side that is to the right of the section A-A′.

It will also be appreciated that references to “left” and “right”,“first side” and “second side” herein are merely for ease ofunderstanding with respect to the drawings, and that mirror-imageversions of the present apparatus and methods can be made in which theconcepts of “left” and “right”, or “first side” and “second side”, areessentially reversed.

As illustrated in FIG. 4 , the first side wall 100A on the first side ofthe work space 100 is opposite the second side wall 100B on the secondside of the work space 100, and the first gas inlet 101A and the secondgas inlet 101B are respectively positioned at or near the first andsecond side walls 100A, 100B. Further, the first gas outlet 102A ispositioned above the floor of the work space, the position of the firstgas outlet 102A being coincident with the first edge 160′ of the buildbed surface 160, or between the first edge 160′ of the build bed surface160 and the first gas inlet 101A when viewed from above, in plan view.The second gas outlet 102B is positioned above the floor of the workspace, the position of the second gas outlet 102B being coincident withthe second edge 160″ of the build bed surface 160, or being between thesecond edge 160″ of the build bed surface 160 and the second gas inlet101B when viewed from above, in plan view. This positioning of the firstand second gas outlets 102A, 102B may ensure that the gas flow does notdisturb the particulate material on the build bed surface 160 and doesnot cause any dust and/or thermal non-uniformities.

The apparatus 1 further comprises one or more flow devices that areoperable to create a first gas flow F1 between the first gas inlet 101Aand the first gas outlet 102A, and a second gas flow F2 between thesecond gas inlet 101B and the second gas outlet 102B, such as to createrespective first and second gas curtains on the first and second sidesof the work space 100 in use.

The first gas inlet 101A and the first gas outlet 102A are positioned onthe first side of the work space 100 and the second gas inlet 101B andthe second gas outlet 102B are positioned on the second side of the workspace 100 such that the first gas flow F1 from the first gas inlet 101Ais directed towards the first gas outlet 102A and the second gas flow F2from the second gas inlet 101B is directed towards the second gas outlet102B without crossing the build bed surface 160.

The gas flow between the first and second gas inlets 101A, 101B and therespective first and second gas outlets 102A, 102B is created by suctiongenerated at the first and second gas outlets 102A, 102B. The rate ofextraction of the gas by the suction determines the trajectory andtemperature of the gas flow, and is used to create the gas curtains onthe first and second sides of the work space 100. The first gas curtainis due to the first gas flow F1 from the first gas inlet 101A to thefirst gas outlet 102A on the first side of the work space 100, and thesecond gas curtain is due to the second gas flow F2 from the second gasinlet 101B to the second gas outlet 102B on the second side of the workspace 100, as shown in FIG. 4 . The first gas curtain (due to the firstgas flow F1) is formed outward of the first edge 160′ of the build bedsurface 160, or potentially may be aligned with the first edge 160′ ofthe build bed surface 160. The second gas curtain (due to the second gasflow F2) is formed outward of the second edge 160″ of the build bedsurface 160, or potentially may be aligned with the second edge 160″ ofthe build bed surface 160.

As depicted in FIG. 4 , the first and second gas outlets 102A, 102B maybe located in the ceiling 100D of the work space 100 and the first andsecond gas inlets 101A, 101B may be oriented horizontally, substantiallyparallel to the build bed surface 160, or parallel to the floor 100C ofthe work space 100. Further, the first gas outlet 102A is positionedhigher in the work space 100 than the first gas inlet 101A, and thesecond gas outlet 102B is positioned higher in the work space 100 thanthe second gas inlet 101B. The by-products such as dust and fumes of thethree-dimensional printing process have a tendency to move upwards,hence this arrangement of gas inlets 101A, 101B and gas outlets 102A,102B is useful to catch those by-products effectively. Along with theadjustment the flow rate of the flow devices, the gas inlets 101A, 101Band gas outlets 102A, 102B may be arranged in close proximity or thevertical distance between them may be adjusted such that the createdfirst and second gas curtains may be as parallel as possible to thefloor 100C of the work space 100, or as perpendicular as possible to theplane of the build bed surface 160 or to the floor 100C of the workspace 100.

Further, the first gas inlet 101A and the second gas inlet 101B may bepositioned at the same height as one another with respect to the floor100C of the work space 100, or may be located at different heights.However, in some implementations it may be desirable to provide asymmetric arrangement of the first and second gas inlets 101A, 101Babout the intersection A-A′, and to have the first and second gas inlets101A, 101B positioned at the same height and at the same distance fromthe intersection A-A′.

In some implementations the first and second gas outlets 102A, 102B maybe arranged facing downwards towards the floor 100C of the work space100 or towards the work surface 190. The first and second gas outlets102A, 102B may be at right angles to the ceiling of the work space 100.Alternatively, the first and second gas outlets 102A, 102B may bearranged at an acute or an obtuse angle with respect to the ceiling ofthe work space 100. The first and second gas outlets 102A, 102B may bearranged facing towards the first and second inlets 101A, 101B. It maybe advantageous to position the first and second gas outlets 102A, 102Bsuch that the gas flow between the first and second inlets and the firstand second outlets describes a smooth line, so as to achieve smooth gasflow and less turbulence.

Furthermore, the first and the second gas outlets 102A, 102B may bearranged symmetric to the build bed, which may be advantageous forbetter thermal uniformity across the build bed surface 160.Alternatively, the first and second gas outlets 102A, 102B may bepositioned asymmetrically about the section A-A′, which may bebeneficial when the three-dimensional objects being made are of smallsize and formed in the centre of the build bed, or only on one side ofthe build bed surface.

In one variant, the first and second gas outlets 102A, 102B may bepositioned at the same height. In another variant, the first and secondgas outlets 102A, 102B may be positioned at the different heights so asto cause different flow path geometry and different path lengths. In afurther variant, more than one gas outlet may be provided at differentheights on one side of the work space, with respect to the floor of thework space. However, for optimized gas flow conditions, the gas outletis not provided at the same height as the respective gas inlet.

In presently-preferred embodiments the first and second gas outlets102A, 102B are elongate slots, respectively extending along the lengthof (or parallel to) the first and second edges of the build bed surface160 when viewed from above. The elongate slots create parallel gascurtains in the work space, thereby creating substantially parallelpressure zones outward of the first and second edges of the build bedsurface 160. The cross-sectional area of the opening of each elongatedslot may be smaller than the cross-sectional opening area of the firstand/or second gas inlets.

Further, the gas flow provided at the first and second gas inlets mayhave a temperature lower than or equal to a temperature of the build bedsurface 160 such that the gas flow cools the build bed surface byconvection and helps to reduce temperature gradients.

Flow Devices

In one embodiment, as shown in FIG. 5A, both the first gas outlet 102Aand the second gas outlet 102B may be coupled to a common flow device ora common suction device 210. Thus, the flow device or suction device 210is common to both the gas outlets 102A and 102B, and if the flow path isentirely symmetric having the same flow resistance, both the gas outletswill extract gas at the same gas flow rate and speed.

In another variant, instead of having a common flow device for the firstand second gas outlets, a separate flow device may be provided for eachof the first and second gas outlets 102A, 102B, such that apparatus 1has more than one flow device or suction device. More particularly, afirst flow device or suction device 211 may be coupled to the first gasoutlet 102A, and a second flow device or suction device 212 may becoupled to the second gas outlet 102B. Providing independent flowdevices in this manner may be useful to compensate for any asymmetry inthe convection or to compensate for any asymmetry in the thermalprocess. For example, to compensate for thermal asymmetry, the gas flowrate or gas flow speed at one of the flow devices 102A or 102B may bealtered or modified such that the resulting heat convection is the sameon both sides of the work space. Furthermore, separate or independentflow devices may be used to create a differential flow in the two partsof the work space, on either side of the intersection A-A′. Further,with such an arrangement, it is possible to have flow paths havingdifferent flow resistances and the flow devices can be adjusted suchthat the gas outlets can extract gas at different gas flow rates and atdifferent flow speeds.

The one or more flow devices may be controlled electronically by acontroller 500 as shown in FIGS. 5A and 5B, or they may be controlledmechanically by a mechanical switch, lever or valve.

Sensor

The apparatus 1 may comprise a sensor for sensing the temperature of thebuild bed surface. In one example, a thermal camera may be used as asensor for sensing the temperature of the build bed surface 160 bycapturing thermal images of the build bed surface 160.

Further, the apparatus 1 may further comprise a sensor for sensing thetemperature of the gas at the first gas inlet 101A and/or at the secondgas inlet 101B. The sensor(s) may be located in close proximity to thefirst gas inlet 101A and/or to the second gas inlet 101B. Moreover,there may be a sensor for sensing the temperature of the gas at or nearthe first gas outlet 102A and/or at or near the second gas outlet 102B,where “near” means “in close proximity to” (for example a small distancedownstream of) the gas outlet 102A and/or 102B.

Any type of sensor such as a thermal camera, thermocouple, ResistanceTemperature Detector (RTD) or thermistor may be used to measure thetemperature of the build bed surface, gas inlets or gas outlets.

Controller

As shown in FIGS. 5A and 5B, the controller 500 is in communication withthe flow devices 210, 211, 212 so as to control the flow rate of theflow devices 210, 211, 212 actively or passively. In a passive controlmode, the controller 500 may control the flow rate based onpredetermined flow rate values or pre-stored flow rate values in amemory 501 that is coupled to the controller 500. Alternatively, in anactive control mode, the controller 500 may be configured to receive afeedback signal from one or more of the various sensors to determine amodified flow rate at each gas outlet so as to improve temperaturecontrol of the build bed surface 160.

Further, the controller 500 may control one or more flow devices 210,211, 212 so as to control a suction flow rate from the first and/orsecond gas outlets 102A, 102B based on at least one of: the sensedtemperature of the build bed surface, the sensed temperature at thefirst gas inlet 101A and/or the second inlet 101B, or the sensedtemperature at the first gas outlet 102A and/or at the second gas outlet102B. The controller may be configured to control a duty cycle of theone or more flow devices.

In the active control mode, the flow rate may be adjusted or the one ormore flow devices may be switched ON or OFF after any one or more of acertain number of layers of particulate material have been deposited,after a certain number of process sequences, after a certain time haselapsed, or after certain temperature within the work space has reached.For example, if the temperature within the work space 100 exceeds apredetermined threshold value, the suction flow rate of the one or moreflow devices may be increased so as to convey more cool gas into thework space and remove the excess heat.

Furthermore, based on the process conditions and/or temperature withinthe work space 100, the controller may switch OFF the one or more flowdevices for a certain time or until a certain process condition is met,for example until a desired build bed surface temperature has beenachieved within the work space. For example, if the build bed surfacetemperature falls below a predetermined threshold value, the gas flow isnot required to enhance convection of the build bed surface, so thecontroller may switch OFF the one or more flow devices.

When the one or more flow devices are switched OFF, the controller mayprovide an alert signal to the user. Based on this, the user may adjustother parameters or devices in the apparatus 1 so as to maintain thedesired process conditions or desired build bed surface temperature.

The controller may be a computing device, a micro-processor, anapplication-specific integrated circuit (ASIC), or any other suitabledevice to control the one or more flow devices. The controller may be aseparate control board or may be a part of the control circuitry of theapparatus that may be configured to control the functions of variouscomponents such as the sleds, the radiation source assembly, the roller,or the printhead assembly of the apparatus 1.

FIG. 6 , which is similar to FIG. 4 , additionally shows a gas flow dueto convection above the build bed surface 160. The gas flow from theinlets to the respective outlets may be set up so that first and secondgas curtains on the first and second sides of the work space 100 createthree separate pressure zones within the work space 100: two outerpressure zones between each gas inlet and the respective gas outlet, andan inner/central pressure zone above the build bed surface 160. The gascurtains may be set up effectively by controlling the flow rate at thegas outlets and by arranging the gas outlets e.g. in the form ofelongate slots located above either side of the work space 100. FIG. 6illustrates an upward flow of gas on either side of the work space 100that has a significant vertical component in the direction of thenatural convection flow. It thus enhances the natural convection flowthat is set up by the hot build bed surface 160. Within the innerpressure zone, the pressure is lower than in the two outer pressurezones, and due to a fast upward flowing component an upward flow is setup in the inner pressure zone next to each curtain.

The generated three pressure zones may be used to remove excess heatfrom the work space 100 and also to remove impurities or chemicalsubstances such as evaporating fluid agent, smoke, fumes, exhaust gasesand airborne particles from the work space 100. The central pressurezone may experience an updraft along the convection direction therebyenhancing the natural flow of convection.

The properties of the two outer gas flows and the resulting gas curtainsneed not be of the same shape or flow rate, and depend on the work spacedesign and the respective rates of extraction and flow resistances setup by the inlet and outlet and the intervening flow path.

Therefore, the first gas flow F1 may create a first gas curtain on thefirst side of the work space 100 and a first pressure zone outward ofthe first edge 160′ of the build bed surface 160, and the second gasflow F2 may create a second gas curtain on the second side of the workspace and a second pressure zone outward of the second edge 160″ of thebuild bed surface 160. In some implementations, the first pressure zoneand the second pressure zone may have substantially the same pressure.This may ensure that symmetry is maintained within the work space andthus any thermal non-uniformities may be avoided.

Thus, due to the generation of the first and second gas curtains on thefirst and second sides of the work space 100, first and second pressurezones may be created outward of the first and second edges of the buildbed surface 160, and a central pressure zone may be created above thebuild bed surface 160, as shown in FIG. 6 . The central pressure zonemay have a pressure lower than the first pressure zone and the secondpressure zone. The gas flow in the central region of the build bedsurface 160 may have a low flow rate and small volume so as to avoidimpact of a downward gas flow on the build bed surface 160 strong enoughto cause temperature depressions and disturbance of the layer ofparticulate material.

Further, the one or more flow devices may be used to control the gasflow rate or suction speed at the gas outlet. For example, the one ormore flow devices may be configured to control the flow rate of the gasflow such that each pressure zone has a different pressure, or the firstand second zones may have the same pressure. As discussed above, the oneor more flow devices may comprise a suction device that is coupled toboth or each of the first and second gas outlets 102A, 102B, such thatthe first and second gas curtains may be created by operating the one ormore suction devices to apply suction to the first and second gasoutlets 102A, 102B. The one or more suction devices may comprise a fan,or the one or more flow devices may comprise a fan.

It should be appreciated that the suction device is not limited tocomprising a fan. Instead, any external source of suction (such as afactory vacuum device) or any known internal source of suction may beused and may be coupled to the gas outlet, for example by a suitablelength of tube.

Central Gas Duct

In another implementation, a central pressure zone may be created byinjecting a downward flow of low pressure gas into the work space 100and may be provided to the build bed surface 160. The temperature ofthis gas may be lower than the temperature of the gas provided by thefirst and second gas inlets 102A, 102B. The downward gas flow may beadjusted so as to create a small downward flow of gas to the build bedsurface 160. This may provide additional control over the temperature ofthe build bed surface 160. To provide this downward flow of gas, asshown in FIG. 7 , the apparatus 1 may further comprise a gas duct 103Aabove the build bed surface 160 and one or more inflow devices may bearranged to create a downward flow of low pressure gas from the gas duct103A towards the build bed surface 160 in use. The one or more inflowdevices may adjust the downward flow so as to control the flow rate,velocity and/or volume of the gas flow. This downward flow of gas maycreate a central or low pressure zone above the build bed surface 160and can also control the pressure of the central zone. The centralpressure zone may be used to a small degree to cool a portion of thebuild bed surface to make it more uniform thermally, while avoidinggeneration of dust and temperature non-uniformity. The one or moreinflow devices may comprise a fan or an impeller and may be controlledby the controller 500 or by a mechanical switch, lever or valve.

Sleds

In one implementation, the apparatus 1 has two sleds: a distributionsled 130 on which a distribution device such as roller may be mounted,and a print sled 140 on which droplet deposition heads may be mounted.

The two sleds 130, 140 are shown in FIG. 8 in parking positions on thefirst and second sides of the work space 100. The sleds 130, 140 mayhave one or more radiation source assemblies mounted on them, forexample one that may be used for pre heating and one that may be usedfor sintering. Alternatively, the apparatus 1 may have a further sled(not shown) on which a radiation source assembly may be mounted.

During the three-dimensional printing process, the sleds 130, 140 aremoved over the build bed surface 160 to perform their functions duringthe stages of the build process and may be affected by the heat from thenearby radiation source assembly, overhead radiation assembly or bygenerated heat during process within the work space. During the buildprocess, the radiation source assembly or assemblies raise thetemperature of the sled and its components and/or the nearby componentsat least temporarily in the vicinity of the sled. It is thereforedesirable to cool the sleds 130, 140 to avoid any negative impact ofheat on their functionality, for example on the reliability of thedroplet deposition heads.

Accordingly, the gas flow from the first and/or second gas inlets 101A,101B may be directed towards the one or more sleds on which adistribution device, droplet deposition head assembly or radiationsource assembly is mounted, such that the gas flow cools the one or moresleds. This means that, during operation of the apparatus, the gas flowmay be at least temporarily directed towards the one or more sleds asthey intermittently reside in the parking position near the gas inlet.The gas flow may be directed towards a sled in the parking positionand/or along the path of travel of the sleds. As shown in FIG. 8 , thefirst and second gas inlets 101A, 101B may be provided at the same levelabove the floor 100C of the work space 100 as that of the sleds, so thatthe gas flow impacts the sled face and is deflected so that it passesover the top surface and/or along the sides of the sled 130, 140. Thegas flow may thus also assist in cooling of the sled 130, 140.

Arrangement with Guiding Elements

In one implementation of the apparatus 1, the apparatus may comprise oneor more guiding elements 400 that may be arranged between the firstand/or second gas inlet 101A, 101B and the build bed surface 160, forguiding the gas flow from the first and/or second gas inlet 101A, 101Bto the respective first and/or second gas outlet 102A, 102B. One or moreguiding elements may be arranged on the first and/or second sides of thework space 100. This arrangement may reduce strong gas flow componentsdirected towards the build bed surface 160. Moreover, the guidingelements may direct the gas flow and define the path of the gas flowsuch that the temperature and velocity of the gas flow may becontrolled, for example by restricting the free space into which the gasflow may otherwise disperse. The guiding elements may be arranged as afixed structure or alternatively may be arranged as a movable structureso as to guide the gas flow as they are repositioned, for exampledynamically during a build process.

In one implementation shown in FIG. 9 , guiding elements 400 a-400 f arearranged at the first and second sides of the work space 100. Fourguiding elements 400 a, 400 b, 400 c, 400 d are arranged to protrudefrom the ceiling 100D of the workspace, with two guiding elements 400 a,400 b on the first side of the work space 100 and two guiding elements400 c, 400 d on the second side of the work space 100. The guidingelements restrict the free space over which the flow can disperse. Ascan be seen in the example in FIG. 9 , some of the guiding elements 400e, 400 f extend to within close proximity of the floor 100C of the workspace 100, for example half way or more than half way of the distancefrom the ceiling to the level of the build bed surface. Optionally, theguiding elements 400 e, 400 f may be located on the rails 120 on whichthe sleds 130, 140 are mounted. Alternatively, the guiding elements 400e, 400 f may be located outside the area of the rails 120 or between therails 120. In these cases, the parking position of the sleds 130, 140may be shifted appropriately towards the build bed surface.

The guiding elements 400 a-400 d protruding from the ceiling 100D of thework space 100 may be fixed to the ceiling 100D as a fixed structure oralternatively they may be coupled to the ceiling 100D via mechanicalmoveable linkages.

Furthermore, the guiding elements 400 a-400 f may be arranged so as toguide the gas flow in such a way that the formation of the gas curtainscan be enhanced, for example the guiding elements near the outlets maydirect the gas flow to follow an upward direction for at least an upperhalf of the distance between the ceiling 100D and the build bed surface160. Additionally or instead, the guiding elements may be arranged sothat the gas flow reaches to the floor 100C of the work space and to thegas outlet without reaching the build bed surface. Instead of anglingthe inlet, a guiding element may be used to deflect the flow uponentering the working space. As shown in FIG. 9 , the gas flows F1, F2are first deflected by a guiding element 400 e, 400 f respectivelylocated near the gas inlets 101A, 101B so as to direct the gas flowtowards the ceiling 100D of the work space 100 so as to cool the hotareas of the ceiling, then the second guiding elements 400 a, 400 clocated at or near the ceiling 100D respectively direct the gas flowtowards the floor 100C of the work space 100. Next, the guiding elements400 a, 400 b, 400 c, 400 d located near the gas outlets 102A, 102Bredirect the respective gas flows F1, F2 towards the respective gasoutlets 102A, 102B. With this type of arrangement of guiding elements400 a-400 f, a high volume gas flow can be maintained over a definedflow path. For example, the guiding elements 400 e, 400 f guide the gasflow such that the gas flow F1, F2 is deflected to the ceiling of thework space to cool any hot areas in the ceiling of the work space, andthen before extracting the gas flow through the gas outlets 102A, 102Bthe gas flow F1, F2 is deflected from the ceiling 100D of the work space100 to the floor 100C of the work space 100 by the guiding elements 400a, 400 c so as to cool the build bed surface 160 and also to flow acrossthe sleds and remove excess heat from the sled surfaces. In this way,the gas flow may be forced along a path in the work space 100 such thatit passes over the hottest areas on the first and second side of thework space, before extraction.

The guiding elements may be positioned symmetrically about the sectionA-A′ so as to enhance gas flow symmetry on the first and second sides ofthe work space 100, for example in arrangements where the rates ofextraction and the respective flow paths of the first and second sidesare substantially equal.

In one example, the guiding element(s) may comprise one or more bafflesor one or more protrusions from the side wall or from the floor of thework space. The baffles may direct the gas flow towards the respectivegas outlets 102A, 102B. The baffles may be arranged between the firstand/or second edges of the build bed surface 160 and the first and/orsecond gas inlets 101A, 101B. Alternatively, the baffle may be arrangedat or near the first and/or second gas inlet 101A, 101B. The baffle maybe formed by a vertical or angled plate, with respect to the level ofthe build bed surface 160.

In another example, the guiding elements may comprise one or more valvesor vanes. Optionally, there may be one or more guiding elements on eachside of the work space depending on the height of the work space, thedistance between gas inlet and gas outlet, the gas flow velocity, andnumber of elements/devices (e.g. sleds, roller, dosing blade to doseparticulate material to the work surface, etc.) between the build bedsurface and the side wall.

It should be noted that the arrangement of guiding elements in FIG. 9 isfor illustrative purpose only, and other arrangements may be envisagedthat achieve the effect of directing the gas flow.

Furthermore, as the guiding elements restrict the path of the gas flow,they help to control the gas flow velocity by increasing the speed ofgas flow for a fixed rate of suction and to increase the temperatureexchange with the hotter surfaces adjacent the restricted path.Additionally, the guiding structures may be formed of thermallyconductive material so as to remove heat from the gas flow as it passes.

In another implementation, the distribution sled 130 and/or the printsled 140 may function as a dynamic guiding element. As shown in FIG. 8 ,when the distribution sled 130 and the print sled 140 are at the parkingposition, the gas flow may be deflected by the sleds 130, 140 such thatthe gas flow passes over the sleds may partially be deflected to theceiling of the work space, then flow down to the floor of the work spaceand be directed back by the floor of the work space and the outlets102A, 102B towards the ceiling.

In further implementation shown in FIGS. 10A-10B, the gas inlets 101A,101B may be coupled to the gas outlets 102A, 102B via a flexible tube ora pipe which may function as a guiding element to guide the gas flow.The flexible tube may be fully perforated or partially perforated, orotherwise cut away in places. For example, FIG. 10A shows the first gasinlet 101A and the first gas outlet 102A coupled by a partiallyperforated tube 410, with the perforated part of tube 410 facing towardsthe build bed surface 160 such that the gas flow may enter the workspace 100 closer to the build bed surface through the perforations ofthe tube 410 so as to cool the build bed surface 160. The perforatedpart of the tube 410 may be joined to a solid part near the first gasoutlet 102A so as to guide the gas flow towards the first gas outlet102A.

FIG. 10B shows another variant of a flexible tube 420 in which theflexible tube incorporates a slot in the tube wall, through which slotgas may enter the work space. The first gas inlet 101A and the first gasoutlet 101B are coupled by the slotted tube 420 and the slot facestowards the build bed surface 160 such that the gas flow may enter thework space closer to the build bed surface 160 through the slot of thetube 420 so as to cool the build bed surface 160.

It should be noted that FIGS. 10A-10B depict arrangements of differentflexible tubes or pipes at the first side of the work space, only forillustration. However, the second side of the work space may be amirror-image of the first side of the work space for symmetry of the gasflow. For example, a perforated tube 410 can be used on both the firstand second sides of the build bed surface 160, or a slotted tube 420 canbe used on both the first and second sides of the build bed surface 160.Alternatively, a combination of the perforated tube 410 and the slottedtube 420 may be used in the work space 100—for example, the perforatedtube 410 may be arranged on the first side of the work space 100 whilethe slotted tube 420 may be arranged on the second side of the workspace 100.

As shown in FIGS. 3(a) to 3(h) above, in some variants the gas outlet102A may face downwards towards the floor 100C of the work space 100 ortowards the work surface 190. In some of these variants, one or more ofthe gas outlets may be arranged facing downwards and towards therespective gas inlets, and the geometry of the gas outlet may depend onthe geometry of the gas inlet. With these arrangements, a non-turbulentflow path may be created between the gas inlet and the respective gasoutlet.

However, in another variant as depicted in FIG. 11 , the gas outlet 102Amay protrude from the ceiling 100D of the work space 100 and into thework space 100, and the gas outlet 102A may face sidewards towards theside wall 100B of the work space 100. With such an arrangement on eachside of the work space 100, the flow paths on the first and second sidesof the build bed surface 160 may be created such that the gas is forcedtowards the centre of the work space and the flow path comes close tothe edge of the build bed surface 160 before exiting through the gasoutlet, thus resulting in efficient cooling of the build bed surface.This arrangement leads to a more intricate flow path between the gasinlet and the respective gas outlet. For this variant, it may beadvantageous to arrange the gas outlet between the gas inlet and thebuild bed surface (i.e. away from the edge of the build bed surface) sothat the flow path will not disturb the particulate material on thebuild bed surface. It should be noted that in FIG. 11 , the protrusionis shown with one angled side. However, the protrusion is not limited tothis shape, and it may have any shape with the opening on the sidefacing towards the opposite side wall of the work space (i.e. towardsthe side wall which is opposite to the side wall comprising therespective gas inlet 101A). Moreover, the geometry of the protrusion maybe designed according to the required flow path profile.

General Considerations

The reference to “gas” in this disclosure may incorporate atmosphericair, inert gas, nitrogen, a combination of these gases, or any gas thatmay be compatible with the three-dimensional printing process.

It should be appreciated that even though a single gas inlet at or nearthe side wall of the work space has been depicted in the Figures, theinvention is not limited to this and any number of gas inlets asrequired can be envisaged. Moreover, the gas inlets may be simple holesor apertures on the side walls of the work space, and there could be aplurality of holes of different (or same) sizes on the side walls of thework space.

Further, the gas may be provided to the gas inlets naturally, such thateach inlet is in direct communication with the atmospheric air.Alternatively, the gas may be provided to the gas inlets using a flowdevice such as a fan or impeller to draw gas into the gas inlets. Inanother example, the gas may be delivered to the gas inlets using anexternal gas supply device such as a gas cylinder, with the gas beingsupplied from the gas cylinder to the gas inlet at elevated pressure.

Also, it should be noted that, even though a single gas outlet at oneside of the work space has been depicted in the Figures, the inventionis not limited to this and any number of gas outlets as required can beenvisaged.

1. An apparatus for manufacturing a three-dimensional object fromparticulate material, the apparatus comprising: a work space bounded bya first side wall on a first side of the work space, and a second sidewall on a second side of the work space, the first side wall opposingthe second side wall; a build bed having a build bed surface, the buildbed surface being comprised in the floor of the work space and having afirst edge on the first side of the work space, towards the first sidewall, and a second edge on the second side of the work space, towardsthe second side wall; a first gas inlet at or near the first side wall;a second gas inlet at or near the second side wall; a first gas outletabove the floor of the work space, wherein, in a projective view, theposition of the first gas outlet is coincident with the first edge ofthe build bed surface, or is between the first edge of the build bedsurface and the first gas inlet; and a second gas outlet above the floorof the work space, wherein, in a projective view, the position of thesecond gas outlet is coincident with the second edge of the build bedsurface, or is between the second edge of the build bed surface and thesecond gas inlet; wherein the first gas outlet is positioned higher inthe work space than the first gas inlet, and the second gas outlet ispositioned higher in the work space than the second gas inlet; andwherein one or more flow devices are operable to create first and secondgas flows between the first gas inlet and the first gas outlet, andbetween the second gas inlet and the second gas outlet, respectively,such as to create respective first and second gas curtains on the firstand second sides of the work space in use.
 2. (canceled)
 3. (canceled)4. (canceled)
 5. The apparatus according to claim 1, wherein the firstand second gas outlets are located in the ceiling of the work space. 6.The apparatus according to claim 1, wherein the first and the second gasoutlets are elongate slots respectively extending, in a projective view,along the length of the first and second edges of the build bed surface.7. The apparatus according to claim 1, wherein, in use, the first gasflow creates a first pressure zone outward of the first edge of thebuild bed surface, and the second gas flow creates a second pressurezone outward of the second edge of the build bed surface.
 8. Theapparatus according to claim 1, further comprising a gas duct above thebuild bed surface and one or more inflow devices arranged to create adownward flow from the gas duct towards the build bed surface in use,wherein the downward flow is of lower pressure than the first and secondgas flows.
 9. (canceled)
 10. (canceled)
 11. The apparatus according toclaim 1, wherein the one or more flow devices comprises a suction devicethat is coupled to both the first and second gas outlets, such that, inuse, the first and second gas curtains are created by the suction deviceapplying suction to the first and second gas outlets.
 12. The apparatusaccording to claim 1, wherein the one or more flow devices comprise afirst suction device that is coupled to the first gas outlet and asecond suction device that is coupled to the second gas outlet. 13.(canceled)
 14. The apparatus according to claim 1, wherein the first andsecond gas outlets are arranged facing downwards towards the floor ofthe work space.
 15. (canceled)
 16. The apparatus according to claim 1,wherein the first and second gas outlets are arranged symmetricallyabout a build bed axis.
 17. (canceled)
 18. (canceled)
 19. (canceled) 20.The apparatus according to claim 1, further comprising one or moreguiding elements arranged between the first and/or second gas inlet andthe build bed surface, for guiding the gas flow from the first and/orsecond gas inlet to the respective first and/or second gas outlet so asto reduce strong gas flow components directed towards the build bedsurface.
 21. (canceled)
 22. The apparatus according to claim 20, whereinthe guiding elements are arranged on the first and/or second sides ofthe work space.
 23. An apparatus for manufacturing a three-dimensionalobject from particulate material, the apparatus comprising: a work spacebounded by a first side wall on a first side of the work space, and asecond side wall on a second side of the work space, the first side wallopposing the second side wall; a build bed having a build bed surface,the build bed surface being comprised in the floor of the work space andhaving a first edge on the first side of the work space, towards thefirst side wall, and a second edge on the second side of the work space,towards the second side wall; a first gas inlet at or near the firstside wall; a second gas inlet at or near the second side wall; a firstgas outlet above the floor of the work space, and a second gas outletabove the floor of the work space; wherein the first and second gasoutlets are elongate slots respectively extending, in a projective view,along the length of the first and second edges of the build bed surface;wherein the first gas outlet is positioned higher in the work space thanthe first gas inlet, and the second gas outlet is positioned higher inthe work space than the second gas inlet; wherein a first suction deviceis coupled to the first gas outlet and a second suction device iscoupled to the second gas outlet, each suction device being operable tocreate a respective first and second gas flow from the first gas inletto the first gas outlet, and from the second gas inlet to the second gasoutlet, respectively, such as to create respective first and second gascurtains on the first and second sides of the work space, the first gasflow creating a first pressure zone outward of the first edge of thebuild bed surface, and the second gas flow creating a second pressurezone outward of the second edge of the build bed surface; and whereinthe apparatus further comprises a sensor for sensing the temperature ofthe build bed surface.
 24. The apparatus according to claim 1, furthercomprising at least one of: a sensor for sensing the temperature of thebuild bed surface; a sensor for sensing the temperature of the gas atthe first gas inlet; a sensor for sensing the temperature of the gas atthe second gas inlet; a sensor for sensing the temperature of the gas atthe first gas outlet; and sensor for sensing the temperature of the gasat the second gas outlet; and a controller for controlling the one ormore flow devices so as to control a suction flow rate from the firstand/or second gas outlets based on at least one of: the sensedtemperature of the build bed surface; the sensed temperature at thefirst gas inlet; the sensed temperature at the second gas inlet; thesensed temperature at the first gas outlet; and the sensed temperatureat the second gas outlet.
 25. (canceled)
 26. (canceled)
 27. (canceled)28. (canceled)
 29. A method for operating an apparatus for manufacturinga three-dimensional object from particulate material, the apparatuscomprising: a work space bounded by a first side wall on a first side ofthe work space, and a second side wall on a second side of the workspace, the first side wall opposing the second side wall; a build bedhaving a build bed surface, the build bed surface being comprised in thefloor of the work space and having a first edge on the first side of thework space, towards the first side wall, and a second edge on the secondside of the work space, towards the second side wall; a first gas inletat or near the first side wall; a second gas inlet at or near the secondside wall; a first gas outlet above the floor of the work space,wherein, in a projective view, the position of the first gas outlet iscoincident with the first edge of the build bed surface, or is betweenthe first edge of the build bed surface and the first gas inlet; and asecond gas outlet above the floor of the work space, wherein, in aprojective view, the position of the second gas outlet is coincidentwith the second edge of the build bed surface, or is between the secondedge of the build bed surface and the second gas inlet; wherein thefirst gas outlet is positioned higher in the work space than the firstgas inlet, and the second gas outlet is positioned higher in the workspace than the second gas inlet; the method comprising: operating theone or more flow devices to create first and second gas flows betweenthe first gas inlet and the first gas outlet, and between the second gasinlet and the second gas outlet, respectively, such as to createrespective first and second gas curtains on the first and second sidesof the work space.
 30. The method according to claim 29, wherein thefirst gas flow creates a first pressure zone outward of the first edgeof the build bed surface, and the second gas flow creates a secondpressure zone outward of the second edge of the build bed surface. 31.(canceled)
 32. (canceled)
 33. (canceled)
 34. (canceled)
 35. The methodaccording to claim 30, wherein the first pressure zone and the secondpressure zone have substantially the same pressure.
 36. The methodaccording to claim 29, further comprising applying suction to the firstand second gas outlets to create the first and second gas curtains so asto create the first and second gas flows from the first gas inlet to thefirst gas outlet, and from the second gas inlet to the second gasoutlet, respectively.
 37. (canceled)
 38. The method according to claim29, further comprising at least one of: sensing the temperature of thebuild bed surface; sensing the temperature of the gas at the first gasinlet; sensing the temperature of the gas at the second gas inlet;sensing the temperature of the gas at the first gas outlet; and sensingthe temperature of the gas at the second gas outlet; and controlling theone or more flow devices so as to control a suction flow rate at one orboth of the first and second gas outlets based on at least one of: thesensed temperature of the build bed surface, the sensed temperature atthe first gas inlet; the sensed temperature at the second gas inlet; thesensed temperature at the first gas outlet; and the sensed temperatureat the second gas outlet.
 39. (canceled)
 40. (canceled)
 41. (canceled)42. (canceled)
 43. The method according to claim 29, further comprisingdirecting the gas flow towards one or more sleds on which a distributiondevice, a droplet deposition head assembly or a radiation sourceassembly is mounted, such that the gas flow cools the one or more sleds.44. The apparatus according to claim 23, further comprising at least oneof: a sensor for sensing the temperature of the gas at the first gasinlet; a sensor for sensing the temperature of the gas at the second gasinlet; a sensor for sensing the temperature of the gas at the first gasoutlet; and a sensor for sensing the temperature of the gas at thesecond gas outlet; and a controller for controlling one or both of thefirst and second suction devices so as to control a suction flow ratefrom the first and/or second gas outlets based on at least one of: thesensed temperature of the build bed surface; the sensed temperature atthe first gas inlet; the sensed temperature at the second gas inlet; thesensed temperature at the first gas outlet; and the sensed temperatureat the second gas outlet.